The remote control tool LogMeIn Free for Mac [1] was released last week after a few months of beta testing. I wrote about the beta version, which is substantially unchanged in its release, in "LogMeIn Adds Remote Control for Mac [2]" (2007-06-11). The program enables you to connect to any of a group of computers that you have set up or that others have given you access to after the installation of a lightweight client. Minimal configuration is needed once you've registered the software and set up groups of machines.
The software is a little clunky working within a browser window, but it can traverse NAT gateways, a feature that lets you connect to otherwise unreachable computers. Leopard's Screen Sharing feature can tunnel (with inconsistent success), too, via Back to My Mac and iChat AV 4. (Back to My Mac works among a set of computers you register with a single .Mac account; iChat Screen Sharing requires you to grant or request permission for a buddy to see your screen or vice-versa.) For a run-down of other options, see the TidBITS article noted above.
The company, eponymously named LogMeIn, also announced a beta of LogMeIn Rescue with Mac OS X support [3], extending their existing support for Windows. This tool, designed for remote technical support, lets a customer install a tiny applet with zero configuration to allow remote control; the beta includes Mac OS X remote control. The software costs $99 per month per technician, paid as a lump sum of $1,188 for a year's subscription, or $129 per month per support person for a single month's service at a time.
Both products require Mac OS X 10.4 or 10.5.
[1]: https://secure.logmein.com/products/free/mac/Default.asp?lang=en
[2]: http://db.tidbits.com/article/9027
[3]: https://beta.logmeinrescue.com/HelpDesk/Home.aspx